L’influence de l’exploitation forestière sur la concentration des particules dans les petits cours d’eau de la Beauce, Québec

Cette étude a pour but d'évaluer l'influence de l'exploitation forestière sur l'augmentation de la quantité de sédiments en suspension dans cinq cours d'eau soumis à différents types de coupe. Lorsque les exploitations sont effectuées sans aucun souci de protection et que la machinerie forestière a libre accès au cours d'eau, les concentrations des sédiments inorganiques et organiques en suspension se maintiennent respectivement au-dessus de 1 000 et 500 ppm durant la coupe. Les maxima atteignent 197 000 et 65 000 ppm. Lorsque l'on garde la machinerie à une certaine distance des cours d'eau et que les arbres sont abattus en direction opposée, l'augmentation de la concentration de particules en suspension dans l'eau est faible. Il en va de même lorsque les cours d'eau sont protégés par des bandes boisées. Les concentrations des sédiments en suspension dans ces deux derniers cas demeurent généralement sous 35 ppm. Par contre, l'efficacité de la bande boisée est fortement atténuée par les passages de la machinerie, par l'arrivée d'un tributaire bouleversé par les opérations forestières ou par le creusage des tranchées d'égouttement des voies d'accès. Ainsi, les concentrations de sédiments inorganiques et organiques en suspension dépassent fréquemment 100 ppm et atteignent respectivement des maxima de 900 â 2 000 ppm.The influence of logging operations on the input of suspended matters is evaluated on five streams subjected to different logging patterns. When the operations are carried out without protective measures, including tractor crossing of watercourses, the concentrations of inorganic and organic suspended matters remain above 1,000 and 500 ppm respectively during logging. The maxima reach 197,000 and 65,000 ppm respectively. Keeping the tractors away from the streams and felling the trees in the opposite direction of the streams minimize the increase of the suspended load. Similar protection is offered by leaving standing timber strips. These two latter types of protection keep the concentration of suspended sediments below 35 ppm. On the other hand the efficiency of the green strip is greatly reduced by tractors using it, by the crossing of a disturbed tributary, or by the digging of road drains. Thus, the concentrations of suspended sediments frequently go beyond 100 ppm and the maxima reach 900 and 2,000 ppm for the inorganic and organic fraction respectively.Der Einfluss von Waldbautâtigkeit auf die Menge der Schwebstoffe wurde in funf Bachen, in Gebieten mit verschiedenartigen WaIdbaumethoden ausgewertet. Wenn die Arbeit ohne jegliche Schutzmassnahmen vorgeht und die Waldbaumaschinen die Wasserlaufe durchqueren, halt sich das Niveau fur organische und inorganische Schwebstoffe bei jeweils 1000 und 500 ppm, wâhrend des Fallens. Die Maxima erreichen jeweils 197000 und 65000 ppm. Die Maschinen ausserhalb der wasserlaufe zu halten, und die Baume in entgegengesetzter Richtung zum Wasserlauf zu fallen vermindert den Anstieg der Schwebstoffe. Ahnliche Beschutzung wird durch stehen gelassene Waldstreifen erreicht. Diese beiden Beschutzungstypen halten die Konzentration der Schwebstoffe unter 35 ppm. Andererseits wird die Leistungsfahigkeit der grunen Streifen durch Treckeruberquerungen. oder durch das Graben von Entwâsserungskanâlen fur die Wege sehr vermindert. So erhebt sich die Konzentration der inorganischen und organischen Schwebstoffe hâufig auf mehr als 100 ppm und erreicht Maxima von jeweils 900 und 2000 ppm

Water relations of black spruce trees on a peatland during wet and dry years

Low water tables typically found in peatlands during dry summer periods or in the vicinity of drainage ditches may lead to moisture deficiency in porous surface peats. Episodes of drought stress might compromise the growth benefits brought about by lower ground-water levels. We examined the water relations of black spruce (Picea mariana) trees on a natural peatland during relatively wet (1990) and relatively dry (1991) summers. Seasonal patterns of pre-dawn and mid-day shoot water potentials and stomatal conductance were not related to peat water content or to water-table depth. There was no evidence of water stress or osmotic adjustment in sampled trees during wet and dry growing seasons. Our soil moisture data showed that although water-table levels were as low as −66 cm in 1991, water availability in the root zone remained high. Even with the absence of mid-day water stress during the summer of 1991, a 50% reduction in stomatal conductance as compared with the previous year was found. We suggest that signals from the bulk of the roots located in dry peat top layer contributed to the regulation of stomatal conductanc

Cinématique et cinétique de l'accélération en course

Québec Université Laval, Bibliothèque 201

Different ways to support and thwart autonomy : parenting profiles and adolescents’ career decision making

Grounded in self-determination theory, this study aimed to (1) identify profiles of parental autonomy support and control and (2) examine how these profiles predict indicators of adolescents’ career development (i.e., autonomy and competence in career exploration, and indecision). To this end, we used three annual waves of data covering the postsecondary transition: the last two years of secondary school (T1 and T2) and one year after graduation (T3). The sample included 637 French-Canadian adolescents (54% girls; Mage at T1 = 14). Latent profile analyses were conducted to identify parenting profiles at T1 and T2, which were then associated with the indicators of career development at T2 and T3, respectively, while controlling for their autoregressive effects and sociodemographic information. Four comparable profiles were identified at both waves (i.e., Autonomy Supported, Generally Controlled, Mixed, and Guilt Induced), with a fifth profile (i.e., High Expectations) emerging only at T2. As expected, Autonomy Supported adolescents reported the highest levels of autonomy and competence, and the lowest levels of indecision at both T2 and T3. The expected maladaptive nature of the Generally Controlled profile, however, was found only at T3, when this profile of adolescents became clearly differentiated from the autonomy supported profile on their career development outcomes. Regardless of the saliency of one specific controlling strategy, parental control hampered adolescents’ career development, undermining autonomy and competence in career decision making. These findings reiterate the benefits of autonomy support and the costs of parental control in adolescents’ career development particularly in the long run

Accumulation et fonte de la neige en milieux boisé et déboisé

Les auteurs présentent une étude des caractéristiques physiques du couvert de neige en relation avec l'altitude, l'exposition et le couvert forestier. L'expérience s'est déroulée à la forêt Montmorency, sise à 80 km au nord de Québec. Au cours des hivers 1981 et 1982, l'équivalent en eau maximal de la neige, pour l'ensemble du bassin du lac Laflamme, a été de 28 et 29 cm, respectivement. Durant cette période, les mesures effectuées n'ont pas permis de détecter l'effet des faibles différences d'altitude (50 m) sur l'accumulation de la neige. L'équivalent en eau de la neige était maximal dans les milieux découverts et apparaissait plus important sous les jeunes peuplements que sous les vieux. Les jeunes sapinières, entourées d'arbres plus hauts, agissent comme des pièges à neige. L'influence de l'exposition ne ressort que durant la période de fonte, accélérée d'une semaine sur les flancs sud. La fonte en sous-bois dure un mois et demi en moyenne et est écourtée d'une à deux semaines dans les sites découverts. Un modèle de fonte, basé sur les degrés-jours, est finalement adapté. Le coefficient de fonte est rajusté en fonction de deux périodes distinctes par la densité du manteau nival ou les degrés-jours cumulés.A study of physical characteristics of the snow cover in relation to altitude, aspect and forest cover, is presented in this paper. The experimental site is located at Montmorency forest, 80 km north of Québec City. During the winters of 1981 and 1982, the snow water equivalent for the lake Laflamme watershed reached a maximum of 28 and 29 cm, respectively. The effect on snow accumulation by the small elevation range (50 m) was not detectable by our measurements. The snow water equivalent was greatest in open areas and appeared greater under the young than the older stands. The young fir associations, surrounded by higher trees, act as snow traps. The aspect plays a role during the melting period only, which is shortened by one week on south exposures. Snowmeit lasts one and a half month in average under the cover and is shortened by one to two weeks in the open. A snowmeit model, based on degree-days, is finally calibrated. The melt coefficient is readjusted for two periods separated by snow density or cumulative degree-days.Die Autoren legen eine Studie vor, die die Beziehung der physischen Merkmale der Schneedecke zu Hôhe, Himmelsrichtung und Bewaldung untersucht. Der Versuch wurde im WaId Montmorency, der 80 km nôrdlich von Québec liegt, durchgefùhrt. Wàhrend der Winter 1981 und 1982 war das maximale Wasserâquivalent der Schneemenge 28 cm bzw. 29 cm fur das gesamte Becken des Laflamme-Sees. Wahrend dieser Période konnten die durchgefuhrten Messungen keinerlei Einflup der schwachen Hôhenunterschiede (50 m) auf die Menge des angesammelten Schnees feststellen. Das der Schneemenge entsprechende Wasserâquivalent war maximal in den freien Gebieten und schien grosser unter den jungen Baumbestanden als unter den alten. Die jungen Tannenwâlder, die von hôheren Baurnen umgeben sind, wirken wie Schneefallen. Der EinfluB der Himmelsrichtung wird erst wâhrend der Zeit der Schneeschmelze spurbar, die auf den Sudflanken urn eine Woche kùrzer ist. Die Schneeschmelze im WaId dauert im Durchschnitt eineinhalb Monate und ist ein bis zwei Wochen kurzer in den offenen Gelànden. Ein Schneeschmelze-Modell auf der Basis Grade-Tage wird schlieplich geeicht. Der Schmelzkoeffizient wird zwei Perioden angepaBt, die sich durch die Dichte der Schneedecke oder die kumulierten Grade-Tage unterscheiden

Spontaneous self-ordered states of vortex-antivortex pairs in a Polariton Condensate

Polariton condensates have proved to be model systems to investigate topological defects, as they allow for direct and non-destructive imaging of the condensate complex order parameter. The fundamental topological excitations of such systems are quantized vortices. In specific configurations, further ordering can bring the formation of vortex lattices. In this work we demonstrate the spontaneous formation of ordered vortical states, consisting in geometrically self-arranged vortex-antivortex pairs. A mean-field generalized Gross-Pitaevskii model reproduces and supports the physics of the observed phenomenology

Sex differences in glenohumeral muscle activation and coactivation during a box lifting task

Manual material handling is associated with shoulder musculoskeletal disorders, especially for women. Sex differences in glenohumeral muscle activity may contribute to women’s higher injury risk by affecting shoulder load and stability. We assessed the effects of sex (25 women vs 26 men) and lifting load (6 kg vs 12 kg) on muscle activation during box lifting from hip to eye level. Surface and intramuscular electromyography were recorded from 10 glenohumeral muscles. Most muscles were more activated for the heavier box and for women. These effects were larger for ‘prime movers’ than for stabilisers and antagonists. Despite their apparently heterogeneous effects on muscle activity, sex and mass did not affect Muscle Focus, a metric of coactivation. This may be partly related to the limited sensitivity of the Muscle Focus. Nevertheless, sex differences in strength, more than in coactivation patterns, may contribute to the sex imbalance in the prevalence of musculoskeletal disorders

Effect of pelvic stabilization and hip position on trunk extensor activity during back extension exercises on a roman chair

Objective: To assess the effect of pelvic stabilization and hip position on the electromyographic activity of trunk extensors during Roman chair exercise. A secondary objective was to compare genders. Design: Repeated measures. Subjects: Eleven men and 11 women volunteers. Methods: Five trunk flexion-extension cycles for 3 Roman chair conditions: (i) pelvis unrestrained; (ii) pelvis restrained; and (iii) hip at 40° flexion. Electromyographic signals were recorded on the back muscles, as well as on the gluteus maximus and biceps femoris. The percentage of electro¬myographic amplitude relative to the maximal activity was used to assess the level of muscular activation of each muscle group across the exercises. Results: For both genders, the Roman chair conditions did not influence the activity of the back and gluteus muscles. The hip-at-40°-flexion condition significantly reduced the activity of the biceps femoris (average of 4–18%) relative to the other 2 conditions. Gender differences were observed on the activity of the biceps femoris in all Roman chair conditions. Conclusion: The hip-at-40°-flexion condition would allow the Roman chair exercise to train the targeted back muscles more specifically by overloading them over a longer duration in order to induce physiological changes

Biomechanical differences between expert and novice workers in a manual material handling task.

The objective was to verify whether the methods were safer and more efficient when used by expert handlers than by novice handlers. Fifteen expert and fifteen novice handlers were recruited. Their task was to transfer four boxes from a conveyor to a hand trolley. Different characteristics of the load and lifting heights were modified to achieve a larger variety of methods by the participants. The results show that the net moments at the L5/S1 joint were not significantly different (P > .05) for the two groups. However, compared to the novices, the experts bent their lumbar region less ( experts = 54° (SD = 11°) ; novices = 66° (15°) but bent their knees more (experts ≈ 72°( SD ≈ 30°) ; novices ≈ 53°( SD ≈ 33°), which brought them closer to the box. The handler's posture therefore seems to be a major aspect that should be paid specific attention, mainly when there is maximum back loading. Keywords: Manual material handling, lifting, expert, low back load, ergonomic intervention. Statement of Relevance: The findings of this research will be useful for improving manual material handling training programs. Most biomechanical research is based on novice workers, and adding information about the approach used by expert handlers in performing their tasks will help provide new avenues for reducing the risk of injury caused by this demanding physical task. Acknowledgements: The present research project was funded by the Robert-Sauvé Occupational Health and Safety Research Institute (IRSST) of Quebec. Special thanks go to the expert and novice subjects and the industries that participated in this project.